High strain in Bi_0.5Na_0.5TiO₃-based relaxors by adding two modifiers featuring with morphotropic phase boundary

The electric field-induced strain in lead-free piezoceramics is generally limited to less than 0.4%, which hinders their practical applications such as actuator. Herein we report a new composition of 0.94Bi_0.5Na_0.5TiO₃-0.06Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃-xLi_0.06(K_0.5Na_0.5)_0.94NbO₃ (BNT-BCZT-xLKNN) ceramics by adding two modifiers (i.e., Li_0.06(K_0.5Na_0.5)_0.94NbO₃ and Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃) featuring with a morphotropic phase boundary (MPB) into the Bi_0.5Na_0.5TiO₃ system. The BNT-BCZT-0.02LKNN shows a high strain of 0.5% as well as a strain-electric field ratio (S_max/E_max) of 625 pm/V, which is one of the best performances compared with reported lead-free piezoceramics. Rietveld refinement and microstructure analysis confirmed the existence of tetragonal (P4bm) and rhombohedral (R3c) phases, and a small part of ferroelectric domains embedded into relaxors according to the PFM, both facilitating the relaxor-to-ferroelectric transformation under an external electric field. As a result, a high strain is obtained in the BNT-BCZT-LKNN system. Our work provides an effective strategy for designing novel lead-free materials with high strain.